Objectives: The project will attempt to quantitate penetration of the intestinal mucosal barrier by non-digestible particulate matter in weanling, young adult, and old mice. Both conventional and germ-free mice will be utilized. Test particles, 1.5-mum fluorescent and 5.7-mum nonfluorescent latex, will be administered chronically by gavage. 7Be-labeled carbon (a new test particle produced by bombardment of carbon black with high-energy protons) will be given by gavage in single-dose experiments. Morphology of the tissues involved will be studied by light and electron microscopy with emphasis on the region of the small intestine known to be the major site of particle penetration, the Peyer's patches. Methods: Latex content will be determined in residues of solubilized liver, lung, spleen kidney, mesenteric and popliteal lymph nodes, Peyer's patches, and remainder of small intestine. Particles will be counted in appropriate aliquots of resuspended tissue residue or in residue deposited on small filters. Latex uptake and distribution will be determined in groups of mice given latex for 1 to 60 days. Latex retention will be determined in groups of mice given latex for 60 days and sacrificed at intervals up to 10 weeks after the termination of gavaging. Retention and distribution of 7Be-labeled carbon will be determined by scintillation counting of organs from 0 to 336 hrs after a dose of 10 to the 7 cpm. Significance: The project will provide qualitative and quantitative information on the barrier function of the gastrointestinal tract and its changes with age. By determining particle uptake and distribution, factors which influence particle absorption will be elucidated and information on the mode of transport of particles away from the intestine will be gained. By determining particle retention and redistribution in retoculoendothelial tissues, the project will provide information on the risk of exposure to foreign particulate material that might be inflammatory or carcinogenic.